Utility-scale solar sites rarely come with perfectly flat ground. For developers, owners, engineers and EPCs, uneven terrain creates an important design decision: reshape the site through grading or select a tracker system that can accommodate more of the terrain that already exists.
Terrain-following trackers can help reduce grading and site disturbance, but the outcome depends on more than the tracker itself. Survey accuracy, civil design, foundation engineering, pile planning and field quality control must work together from the beginning.
With up to 2° of pile-to-pile terrain variation, ARRAY OmniTrack® is designed to follow changing terrain while supporting a coordinated path from design through installation. Its project-specific performance depends on how well the team connects the terrain model, grading plan, foundation design and field execution.
That coordination was a central theme of ARRAY’s webinar, The Terrain-Following Blueprint: Design Essentials for Seamless Installation. Experts from ARRAY, Kimley-Horn and Burns & McDonnell shared perspectives on how project teams can reduce surprises and create a more predictable installation process.
The following five practices summarize the discussion for developers, owners, third-party engineers and EPCs evaluating terrain-following tracker projects.
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- Start with the most accurate survey possible.
- Develop the grading plan and tracker profile together.
- Optimize earthwork, foundations and steel as one system.
- Reconcile the pile plan with actual post-grading conditions.
- Verify piles before tracker assembly begins.
Before and after graphic showing the design face, actual post-grading conditions and updated pile plans.
Start With the Most Accurate Survey Possible
Survey data is one of the most important inputs for a terrain-following project. Early in development, it helps teams assess whether terrain-following technology is appropriate for the site and identify where construction may be most practical.
As design advances, survey data informs hydrology, grading plans and pile elevations. Closer to construction, it becomes the basis for the pile plan. Because tracker geometry is tied to the surveyed surface, the consequences of inaccurate or outdated data become more significant as the project progresses.
During the webinar, Jon Manning of Kimley-Horn explained that survey accuracy can vary based on the collection method, ground cover, survey age and data-processing methods. LiDAR, photogrammetry, ground surveys, and other methods may each be appropriate in different circumstances. The important step is to understand the limitations of the available data and communicate them to the engineer of record.
The goal is not simply to obtain survey data. Teams should determine whether the data is accurate enough for the current design phase and plan for additional surveying or design updates when it is not. A reliable terrain model gives the project team a stronger basis for evaluating grading, foundations, and tracker geometry.
Develop the Grading Plan and Tracker Profile Together
Terrain-following technology can reduce grading associated with tracker constraints, but it does not eliminate the need for civil design. A grading plan must also account for roads, drainage, erosion control, earthwork balancing, local requirements, and general constructability.
The grading plan is where civil design and terrain-following technology come together. Civil engineers work with tracker and pile-planning inputs to determine where grading is required, while structural and foundation engineers evaluate pile heights, reveal requirements and foundation assumptions.
This process is iterative. As the grading plan develops, the team should confirm that the proposed surface remains compatible with the tracker’s flexure, height, and structural constraints. If it does not, engineers can evaluate whether to adjust the grading plan, tracker profile, foundation design, or another project variable.
Preliminary cut-and-fill estimates based only on tracker geometry may not represent the project’s final grading quantities. Beginning coordination early gives the team more options to evaluate those tradeoffs before the design becomes difficult or expensive to change.
Tracker installation in the field. Photo and slide provided by Burns & McDonnell.
Optimize Earthwork, Foundations and Steel as One System
Terrain-following design is not about minimizing one quantity at the expense of everything else. Project teams are balancing:
- Earthwork and site disturbance
- Tracker flexure
- Minimum and maximum pile reveal
- Pile lengths and steel tonnage
- Foundation requirements
- Procurement and staging
- Installation tolerances
- Field constructability
Changing one variable can affect several others. From an EPC perspective, Drew Powers of Burns & McDonnell emphasized the importance of balancing material efficiency with a crew’s ability to install the system successfully.
A choice that reduces grading may increase pile quantities or steel tonnage. A choice that reduces steel may create more variation for procurement and installation. The best combination is site-specific and depends on terrain, geotechnical conditions, schedule and installation approach.
The webinar examples showed why foundation engineering and constructability should be part of the conversation early. Ordering every pile to an individually optimized length may reduce theoretical steel quantities, but too much variation can make piles more difficult to stage, distribute and install.
3D Model results for terrain following tracker showing the design torque tube profiles on top of a provided terrain surface.
3D Model results for terrain following tracker showing the design torque tube profiles on top of a provided terrain surface. Red areas = proposed grading areas to meet required tracker heights.
Update the Pile Plan with Actual Post-Grading Conditions
For OmniTrack projects, the pile plan is a critical connection between the engineered tracker profile and the physical site. In practical terms, it defines where each pile should be installed and establishes the intended profile of the tracker row.
The pile-planning process typically develops through four stages:
- Preliminary terrain analysis: The team evaluates the existing terrain and develops an initial tracker profile.
- Grading and design coordination: Civil, structural, and foundation engineers refine the grading plan, tracker layout, and foundation assumptions together.
- Final design and pile procurement: Once the design and grading plan are sufficiently advanced, the team establishes pile requirements and procures the materials.
- Post-grading survey and pile-plan adjustments: After grading is complete, the as-built survey is compared with the surface used to develop the pile plan. Engineers then determine whether updates are needed before pile installation.
The fourth stage is important because the finished surface may not match the digital model perfectly, and the original survey may not represent every area of the site accurately.
If the final surface falls outside the design assumptions, engineers may need to adjust the pile plan and confirm that the revised tracker profile, pile types and reveal heights remain compliant. Depending on the discrepancy, the team may evaluate pile reallocation, limited additional grading or additional engineering analysis.
Drew went on to explain that pile procurement often occurs before the post-grading survey because of material lead times. His recommendation was to avoid ordering pile lengths “to the bone” and to build an appropriate buffer into the procurement strategy. That buffer should be balanced against the cost and complexity of excess steel.
The benefits that targeting pile locations and elevation can reveal when it comes to foundations specifically pile quantities and reveal & retaps. Photo and slide provided by Burns & McDonnell.
Verify Piles Before Tracker Assembly Begins
GPS-equipped pile-driving equipment can use design coordinates to help crews target pile locations and elevations. It can also provide field data that helps teams monitor production and identify potential issues during installation.
GPS installation does not replace quality control. Before tracker assembly begins, teams should check pile elevation, horizontal position, plumb and twist against applicable project and manufacturer requirements. Correcting an outlier while pile-driving equipment is still available is generally simpler than addressing the same issue after torque tubes and other components are installed.
As Drew emphasized, quality control should be part of installation, not just a final inspection. Verifying piles before tracker assembly helps the team identify and address misalignment while the work remains accessible.
For the technical requirements, tolerances and field verification methods that support this process, see the ARRAY OmniTrack® Foundation Guide.
Designing Around The Site
Terrain-following technology changes more than the shape of a tracker row. It changes how surveyors, civil engineers, structural and foundation engineers, procurement teams, tracker manufacturers and EPCs coordinate their work.
The central lesson is simple: terrain-following performance depends on more than tracker flexure. It depends on how early and effectively the project team connects survey data, grading, foundations, pile planning, and field verification.
When these decisions are coordinated, terrain-following trackers can help teams evaluate opportunities to reduce site disturbance, optimize materials, and create a more predictable path from design to installation. The actual benefits remain site- and project-dependent, but the engineering principles apply broadly
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